Rechargeable batteries such as solid state and thin film batteries are used to supply stored energy in many applications, including portable electronics, automotive and cordless tool applications, medical devices, and even space systems. Thin film batteries are solid state batteries (absent liquid electrolytes) having thin films with thicknesses of less than 100 microns. Thin film batteries are used in applications requiring a small size, high specific energy or density, and resistance to environmental degradation. Both solid state and thin film batteries can have battery component films comprising lithium-containing compounds that can include one or more of a current collector, cathode, anode and electrolyte, and which cooperate to store energy. The lithium-containing films are formed on the substrate by conventional fabrication processes, such as for example, physical or chemical vapor deposition (PVD or CVD), oxidation, nitridation, electron beam evaporation, and electroplating processes.
In lithium batteries, some of the battery component films are composed of lithium-containing material, such as lithium metal oxide or other lithium-containing compounds. For example, the cathode can be composed of a lithium-containing material such as LiCoOx. Increasing the thickness of the lithium oxide cathode film increases the energy density of the battery as the thicker cathode film provides greater charge retention and faster charging and discharging. For example, specific energy levels of at least 250 Whr/L can be achieved using a sputtered cathode film having a thickness of 5 microns or higher, as for example, taught in commonly assigned U.S. patent application Ser. No. 11/007,362 entitled “THIN FILM BATTERY AND METHOD OF MANUFACTURE” which is incorporated by reference herein in its entirety. The lithium oxide cathode film can be deposited as an amorphous or microcrystalline film in a sputtering process, and thereafter, crystallized by heating the film; or deposited in a sequence of thin films to form a thicker cathode comprising a stack of films.
However, conventional lithium oxide sputtering processes have several limitations, which include relatively slow film deposition rates that make it economically difficult to manufacture thick cathode films. For example, conventional radio frequency magnetron sputtering processes often result in deposition rates of around 0.2 microns per hour. Increasing the sputter deposition rates can result in plasma arcing which affects the quality of deposited films. Multiple target sputtering processes have been developed to increase deposition rates to achieve thicker cathode layers as for example described in commonly assigned U.S. patent application Ser. No. 11/849,959, filed: September 4, entitled “MANUFACTURING METHOD FOR THIN FILM BATTERY” which is incorporated herein by reference in its entirety. However, even these processes have difficulties as the sputtering properties of different, individual targets often do not match one another resulting in non-uniform deposition across the area of the substrate.
For various reasons that include these and other deficiencies, and despite the development of various battery fabrication methods, further improvements in the sputtering of lithium-containing materials for battery fabrication and related apparatus are continuously being sought.